/Engine/Source/Runtime/Slate/Public/Framework/Application/SlateApplication.h
a pointer to the Widget that currently has the users focus; Empty pointer when the user has no focus.
virtual [TSharedPtr](API\Runtime\Core\Templates\TSharedPtr)< [SWidget](API\Runtime\SlateCore\Widgets\SWidget) > GetUserFocusedWidget ( uint32 UserIndex ) const